Its the difference in ambient from shop temp.....but they dont say what shop temp is....but say its 70 degrees. You would set placard temp if they were cold and it was 70 degrees outside (ambient)
Thanks, I misread that bit, but its still very dumb.
Why even have the chart show a delta range of 108 degrees if thats supposed to be the shop variability?
I don't know of any HVAC system good enough to lower the temp of any building more than 30-40 degrees from ambient at the absolute most on the cooling end unless the area is completely hermetically sealed and insulated, maybe if your shop is in Antarctica it might be relevant form a heating perspective.
Either way this is entirely unscientific and doesnt take into account how long its been in the workshop, and what temperature the air is that you will be filling the tire with and makes a lot of assumptions about the ambient "seasonable" temp range. Also doesn't account for the most likely scenario of highway driving, and sitting before being pulled into workshop, which is how it will be done 90% of the time.
A much better way to do this would be to just measure to Fing temp of the tire... which takes 1 second and is in realtime.. Then set a benchmark for "cold" at ambient which would take a couple of more seconds looking at a thermometer.
You could actually achieve some form of scientific precision that way without making a bunch of assumptions since we can calculate thermal expansion of air or nitrogen.
No wonder the dealer never gets it right, if they are even trying they are using this garbage TSB.
EDIT: BTW my BMW M4 actually gave the TPMS temp reading from inside the tire on the instrument cluster. No need for any BS.
